Answer:
C. a hot-air heating system.
Explanation:
The warm( or hot) air heating system uses a vent to pull in heat from the outside air and heats it over a gas flame. This warm air circulates via ducts, vents or grills which are located throughout the home. This heating systems are often managed by a thermostat.
So
Heat from burning fuel warms the walls of the firebox section of the furnace in
a hot-air heating system.
Option C is correct
